Signal processor

ABSTRACT

When, through a multi-speaker of a DVD audio system, signals are recorded/reproduced using a sampling frequency different for every channel, the quantity of calculation of a filter circuit is reduced. Up-sampling information about whether or not the sampling is carried out before the up-sampling by up-sampling means ( 2   a   , 2   b ) is acquired by up-sampling information detecting means ( 6 ). The signal up-sampled is filtered by a halfband filter circuit ( 3 ), subjected to loss-less compression, and recorded on a recording medium ( 8 ).

TECHNICAL FIELD

The present invention relates to a signal processing apparatus and, moreparticularly to a signal processing apparatus which reduces operationamount in decoding when reproducing a plurality of signals of differentsampling frequencies.

BACKGROUND ART

According to a DVD audio standard for a DVD-based audio disc, itsstorage capacity is 4.7 GB. DVD audio recording scheme is PCM, like CDor DVD-ROM and, as for its specification, a sampling frequencyindicative of fidelity to original sound with which audio is recorded is192 KHz at maximum, which is about 4.3 times as high as that (44.1 KHz)of the CD. This enables to record audio of highest quality.

FIG. 3 is a diagram showing conception of a sound field formed byreproduced DVD audio. In the figure, reference numeral 40 denotes acenter speaker, and 41 a and 41 b denote left and right speakers placedat the left of the center speaker 40 and at the right of the same,respectively. Reference numerals 42 a and 42 b denote left and rightsurround speakers placed behind an auditor, for increasing realism, and43 denotes a speaker called “sub-woofer”, for outputting relatively lowsound. According to the DVD audio standard, reproduction can beperformed by using 6 speakers (6 channels) even when samplingfrequencies and the numbers of quantization bits of respective channelsdiffer from each other. For instance, in configuration shown in FIG. 3,the center speaker 40 and the left and right channel speakers 41 a and41 b for which relatively high sound quality is demanded, performreproduction at 96 KHz, while the left and right surround speakers 42 aand 42 b and the sub-woofer 43 for which relatively high sound qualityis not demanded, perform reproduction at 48 KHz.

By the way, when data of respective channels are to be recorded at 96KHz and in 24 bits for data of 6 channels, a standard for a maximumtransfer rate would be exceeded. Accordingly, it becomes necessary tocompress data when recorded. A compression method includes irreversiblecompression using a psychoacoustic model for use in MPEG or AC3, and“Lossless compression” which is capable of completely restoring data tothe state before compression by employing entropy coding as reversiblecompression, such as Huffman coding. In order to reproduce audio of highquality with fidelity to original sound as described above, the Losslesscompression is desirably employed. This enables to reproduce audio ofhigh quality of 6 channels at 96 KHz and in 24 bits, in data transfer ofthe DVD audio. On the other hand, even when the standard for the maximumtransfer rate is not exceeded, the Lossless compression enables torecord data of 4.7 GB for a long time period.

FIG. 4 is a block diagram showing a conventional DVD audio recordingapparatus. For the sake of simplicity, 3 channels are illustrated,although 6 channels are actually used. In FIG. 4, reference numerals 51a and 51 b denote upsampling means which receive signals of the channels2 and 3 at sampling frequencies of 48 KHz, and adapt their respectivesampling frequencies to 96 KHz for the channel 1. Reference numeral 50denotes a timing delay unit for delaying the signal of the channel 1while the signals of the channel 2 and 3 are upsampled, and 52 denotes afilter circuit for filtering the upsampled signals of the channels 2 and3 and performing interpolation for them so that they are smoothed.Reference numeral 54 denotes Lossless compression means for performingreversible compression of the signals of the channels 2 and 3 whichpassed through the filter circuit 52 and the signal of the channel 1delayed by the delay unit 50. Reference numeral 53 denotes formattransformation means for transforming a Lossless-compressed signal intodata having a predetermined format which can be written to a recordingmedium 56, and 55 denotes recording means for recording the compresseddata into the recording medium 56.

To upsample the sampling frequencies of the signals of the channels 2and 3 from 48 KHz to 96 KHz, respectively, with the above-mentionedconstruction, the upsampling means 51 a and 51 b insert a predeterminednumber of “zeros” into data so that the sampling frequencies are twicehigher (48×2=96), and then a filter circuit 52 having a given factor ina subsequent stage replaces the inserted “zero” samples with :samplesused for smooth interpolation. To be specific, the upsampling processfor inserting the samples having “zero” values into the data of thesignals of the channels 2 and 3 is performed so that the sample havingthe “zero” value is placed in every other sample of the data. While thesignals of the channels 2 and 3 are upsampled, the signal of the channel1 is delayed by the delay unit 50. Instead of the above “0” insertion,processing performed by the upsampling means 51 a and 51 b may be asample holding process which holds a predetermined number of previoussample data or an interpolation process using straight lines rather than“zeros”. Here, in the sample holding process, the data of the signals ofchannels 2 and 3 are interpolated so that after each of the samplesconstituting that data, a sample having the same value as that sample isplaced. For the filter circuit 52, a low pass filter can be realized bya filter such as an FIR (Filter Impulse Response) or an IIR (InfiniteImpulse Response). The filter circuit 52 filters the signals output fromthe upsampling means 51 a and 51 b by using the above filter.

The outputs of the filter circuit 52 and the output of the delay unit 50are processed by the Lossless compression means 54 and then processed bythe format transformation means 53, and the resulting data is written tothe recording medium (DVD audio disc) 56 by using the recording means55.

To read so created data from the recording medium 56 to reproduce audio,a reproducing apparatus shown in FIG. 5 is used. In FIG. 5, referencenumeral 60 denotes reading means for reading data from the recordingmedium 56, and reference numeral 62 denotes formatinverse-transformation means for transforming the read data(Lossless-compressed) into a signal (Lossless-compressed) having aformat of reproducible audio signal. Reference numeral 61 denotescompressed-data decompression means for decompressing the data(Lossless-compressed) which has been subjected to the formatinverse-transformation, and reference numeral 63 denotes a filtercircuit for downsampling predetermined decompressed data as required.

To reproduce the predetermined data decompressed by the compressed-datadecompression means 61 at a sampling frequency of 48 KHz downsampledfrom 98 KHz, with the above-described construction, the filter circuit63 downsamples this data.

In the conventional signal processing apparatus so constructed, thefilter circuit temporarily equalizes the sampling frequencies of theplurality of signals at a recording time, to be recorded in therecording medium, while the filter circuit at a reproducing end changesthe sampling frequencies of the predetermined channels into thepredetermined sampling frequencies, to output the signals.

In this case, when high precision is required for the filter circuitsused in the above processing, the amount of operation therein isnoticeably increased, and burden on hardware is correspondinglyincreased. In addition, the processed signals are reproducedunsatisfactorily.

The present invention is directed to solving the above problem, and anobject of the present invention is to provide a signal processingapparatus which is capable of reducing operation amount in filtercircuits when processing a plurality of signals of different samplingfrequencies, and reproducing all the signals completely.

DISCLOSURE OF THE INVENTION

According to aspect 1 of the present invention, there is provided asignal processing apparatus for encoding a plurality of channel signalsof different sampling frequencies to be recorded in a recording medium,comprising: upsampling means for transforming a sampling frequency of achannel signal having a small sampling frequency among the plurality ofchannel signals of different sampling frequencies into a samplingfrequency of a channel signal having a large sampling frequency; a halfband filter that receives the channel signal upsampled by the upsamplingmeans as an input; and format transformation means for transforming thechannel signal processed by the half band filter and the channel signalhaving the large sampling frequency into signals having predeterminedformats.

According to aspect 2 of the present invention, the signal processingapparatus of aspect 1, further comprises: data compression means forperforming Lossless compression to the signal processed by the half bandfilter and the channel signal having the large sampling frequency.

According to aspect 3 of the present invention, the signal processingapparatus of aspect 1, further comprises: upsampling informationdescription means for describing upsampling information indicating thata sample of the channel signals processed by the half band filter is asample before the upsampling, into a predetermined area of the recordingmedium.

According to aspect 4 of the present invention, there is provided asignal processing apparatus for performing decoding to reproduce datarecorded in a recording medium, said data being recorded in therecording medium after a sampling frequency of at least one channelsignal among a plurality of channel signals of different samplingfrequencies is upsampled, and the resulting channel signal is processedby a half band filter and then transformed into a signal having apredetermined format, comprising: data reading means for reading datafrom the recording medium; format inverse-transformation means forinversely transforming the data read from the data reading means into asignal having a predetermined format; downsampling means fordownsampling a sampling frequency of a specified signal among the formatinverse-transformed signals; and downsampling control means forinstructing the downsampling means to intermittently read the specifiedsignal among the format inverse-transformed signals.

According to aspect 5 of the present invention, in the signal processingapparatus of aspect 4, the signal read by the data reading means iscompletely reproducible data which has been subjected to Losslesscompression, and the apparatus further comprises: data decompressionmeans for decompressing compressed data into data before compressionafter it is subjected to format inverse-transformation.

According to aspect 6 of the present invention, the signal processingapparatus of aspect 4, further comprises: upsampling informationextraction means for detecting upsampling information indicating thatdata is a sample before upsampling performed by the upsampling meanswhen detecting the upsampled signal data; and downsampling control meansfor instructing the downsampling means to intermittently read the dataaccording to the information.

According to aspect 7 of the present invention, in the signal processingapparatus of aspect 6, the upsampling information is recorded in apredetermined area of the recording medium as an information indicatingdata is a sample before upsampling performed by the upsampling means,and the downsampling means reads one of odd-numbered data andeven-numbered data according to the upsampling information, thereby toperform said intermittent reading.

As described above, according to aspect 1 of the present invention,there is provided a signal processing apparatus for encoding a pluralityof channel signals of different sampling frequencies to be recorded in arecording medium, comprising: upsampling means for transforming asampling frequency of a channel signal having a small sampling frequencyamong the plurality of channel signals of different sampling frequenciesinto a sampling frequency of a channel signal having a large samplingfrequency; a half band filter that receives the channel signal upsampledby the upsampling means as an input; and format transformation means fortransforming the channel signal processed by the half band filter andthe channel signal having the large sampling frequency into signalshaving predetermined formats. Therefore, the operation amount of thefilter in upsampling can be reduced about by half.

According to aspect 2 of the present invention, the signal processingapparatus of aspect 1, further comprises: data compression means forperforming Lossless compression to the signal processed by the half bandfilter and the channel signal having the large sampling frequency.Therefore, much data can be recorded in the recording medium withoutdegrading sound quality.

According to aspect 3 of the present invention, the signal processingapparatus of aspect 1, further comprises: upsampling informationdescription means for describing upsampling information indicating thata sample of the channel signal processed by the half band filter is asample before the upsampling, into a predetermined area of the recordingmedium. Therefore, when reproducing a signal from the recording mediumlater, an original shape of the upsampled signal can be recognized, anddata can be read intermittently with reliability.

According to aspect 4 of the present invention, there is provided asignal processing apparatus for performing decoding to reproduce datarecorded in a recording medium, said data being recorded in therecording medium after a sampling frequency of at least one channelsignal among a plurality of channel signals of different samplingfrequencies is upsampled, and the resulting channel signal is processedby a half band filter and then transformed into a signal having apredetermined format, comprising: data reading means for reading datafrom the recording medium; format inverse-transformation means forinversely transforming the data read from the data reading means into asignal having a predetermined format; downsampling means fordownsampling a sampling frequency of a specified signal among the formatinverse-transformed signals; and downsampling control means forinstructing the downsampling means to intermittently read the specifiedsignal among the format inverse-transform ed signals. Therefore,downsampling can be implemented by only performing intermittent reading,and thereby a filter at a reproducing end is dispensed with, whichsignificantly reduces operation amount.

According to aspect 5 of the present invention, in the signal processingapparatus of aspect 4, the signal read by the data reading means iscompletely reproducible data which has been subjected to Losslesscompression, and the apparatus further comprises: data decompressionmeans for decompressing compressed data into data before compressionafter it is subjected to format inverse-transformation. Therefore, whenreproducing the compressed data, its sound quality is not degraded atall.

According to aspect 6 of the present invention, the signal processingapparatus of aspect 4, further comprises: upsampling informationextraction means for detecting upsampling information indicating thatdata is a sample before upsampling performed by the upsampling meanswhen detecting the upsampled signal data; and downsampling control meansfor instructing the downsampling means to intermittently read the dataaccording to the information. Therefore, an original shape of theupsampled signal can be recognized, and data can be read intermittentlywith reliability.

According to aspect 7 of the present invention, in the signal processingapparatus of aspect 6, the upsampling information is recorded in apredetermined area of the recording medium as an information indicatingdata is a sample before upsampling performed by the upsampling means,and the downsampling means reads one of odd-numbered data andeven-numbered data according to the upsampling information, thereby toperform said intermittent reading. Therefore, the signal can be easilydownsampled with a simple circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram principally showing an encoding circuit of asignal processing apparatus according to a first embodiment of thepresent invention.

FIG. 2 is a block diagram principally showing a decoding circuit of thesignal processing apparatus of the first embodiment.

FIG. 3 is a diagram showing conception of reproduction using 6 speakersof multi channels according to a DVD audio standard.

FIG. 4 is a block diagram principally showing an encoding circuit of aconventional signal processing apparatus.

FIG. 5 is a block diagram principally showing a encoding circuit of aconventional signal processing apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1

FIG. 1 is a block diagram showing an encoding circuit of a signalprocessing apparatus according to a first embodiment of the presentinvention. In FIG. 1, reference numerals 2 a and 2 b denote upsamplingmeans which receive signals of channels 2 and 3 at sampling frequenciesof 48 KHz and increase the sampling frequencies, and reference numeral 1denotes a timing delay unit for delaying a signal of a channel 1 whilethe signals of the channels 2 and 3 are upsampled. Reference numeral 5denotes a half band filter circuit for filtering the upsampled signalsof the channels 2 and 3 to eliminate unnecessary band signals of thechannels 2 and 3, resulting from processing by the upsampling means 2 aand 2 b, and reference numeral 3 denotes data compression means(Lossless compression means) for performing reversible compression ofthe signals of the channels 2 and 3 which passed through the half bandfilter circuit 3 and the signal of the channel 1 output from the delayunit 1. Reference numeral 4 denotes format transformation means fortransforming compressed data into data having a prescribed formatwritable to a recording medium 8, and reference numeral 7 denotesrecording means for recording the compressed data into the recordingmeans 8. Upsampling information generation means 6 generate upsamplinginformation about upsampling performed by the upsampling means 2 a and 2b and output the upsampling information to the recording means 7. In theabove construction, the upsampling information generation means 6 andthe recording means 7 constitute upsampling information descriptionmeans.

To upsample the sampling frequencies of the signals of the channels 2and 3 from 48 KHz to 96 KHz with the above construction, the upsamplingmeans 2 a and 2 b insert a predetermined number of “zeros” into datacorresponding to the signals of channels 2 and 3 so that the samplingfrequencies are twice higher (48×2=96), respectively. Meanwhile, thesignal of the channel 1 is delayed by the delay unit 1 during aspecified time period. Then, the half band filter circuit 3 in asubsequent stage performs interpolation of the signals of the channels 2and 3. The half band filter has an FIR (Finite Impulse Response) factor,for example, (C, 0, B, 0, A, 1, A, 0, B, 0, C), which are arrangedsymmetrically such that two factors are adjacent to a reference value“1” placed at the center thereof, and from each of the two factors, “0”and a factor alternately appear. With the use of this, the upsampleddata is processed.

Also, the upsampling information generation means 6 generates theupsampling information indicating whether or not data is sample databefore upsampling performed by the upsampling means 2 a and 2 b.

So processed data is output from the half band filter circuit 3, andprocessed by the Lossless compression means 5 and then processed by theformat transformation means 4, to be written on the recording medium(DVD audio disc) 8 by using the recording means 7. (As an example of theabove format transformation, there is transformation into a Pack/Packetstructure according to an MPEG standard system.) The recording means 7writes the compressed data and the upsampling information (indicatingwhether or not the data is sample data before upsampling and the like)generated by the upsampling information generation means 6 intopredetermined areas of the recording medium 8. The predetermined areascan be private headers according to DVD audio standard.

To read so created data from the recording medium 8 to reproduce audio,a reproducing apparatus shown in FIG. 2 is used. In FIG. 2, referencenumeral 20 denotes reading means for reading data from recording medium8, and 21 denotes upsampling information extraction means for readingthe upsampling information corresponding to the data read by the datareading means 20 from the predetermined area of the recording medium 8.Reference numeral 23 denotes format inverse-transformation means fortransforming the read data (Lossless-compressed) into theLossless-compressed audio data and header information such as thesampling frequency, and 22 denotes compressed-data decompression meansfor decompressing the data (Lossless-compressed) which has beensubjected to the format inverse-transformation. Reference numeral 24denotes downsampling means for downsampling the upsampled signals, and25 denotes downsampling control means for controlling operation of thedownsampling means according to the upsampling information. As anexample of the above format inverse-transformation, there istransformation from the Pack/Packet structure according to the MPEGstandard system to the Lossless-compressed data and the header such asthe sampling frequency.

The data read from the recording medium 8 with the above construction istransformed into the Lossless-compressed audio data and the headerinformation by the format inverse-transformation means 23, and theninput to the compressed-data decompression means 22, where theLossless-compressed data is decompressed to restore the data to theirstates before compression, and the resulting signals of the respectivechannels are output.

Then, in accordance with an instruction of the downsampling controlmeans 25, data is intermittently read. When the data corresponding tothe signals of the channels 2 and 3 are read, and flags indicating thatsample data of the channels 2 and 3 are sample data before upsamplingperformed by the upsampling means 2 a and 2 b are obtained from theupsampling information extracted by the upsampling informationextraction means 21, the downsampling means 24 operates so as to readonly the sample data before upsampling of the signals of the channels 2and 3.

The upsampling information output from the upsampling informationextraction means 21 is input to the downsampling control means 25. Thedownsampling control means controls the downsampling means 24 accordingto the upsampling information so that it downsamples the samplingfrequencies of the signals of the channels 2 and 3 which have beensubjected to the format inverse-transformation from 96 KHz into 48 KHz.

Thus, in accordance with this embodiment, the upsampling informationindicating whether or not data are sample data before upsamplingperformed by the upsampling means 2 a and 2 b, are generated, and theupsampled signals are filtered by the half band filter circuit 3 andthen Lossless compressed, to be recorded in the recording medium 8.Therefore, operation amount in filtering when upsampling the signals canbe reduced by half as compared with a case using a conventional filter.In addition, since when reproducing the data, reading is performed everyother data intermittently with referring to the upsampling information,the downsampling processing at the reading can be performed by simplyintermittently reading data. Hence, a filter circuit used inreproduction is dispensed with unlike the conventional example, and theoperation amount in downsampling can be reduced. Further, whendownsampling the signals at the reproduction, original data (sampledata) can be restored completely.

While in this embodiment the upsampling information are written in thepredetermined areas of the disc for each data, the areas into which dataare to be inserted at upsampling may be previously determined, whetheror not first data is inserted data may be uniformly decided, and on thebasis of that result, intermittent reproduction may be performed byfirmware processing.

While in this embodiment the half band filter is used, this may bereplaced by an FIR filter or an IIR filter, which changes only theinserted sample data instead of changing original sample data in theupsampling, whereby the original data (sample data) can be completelyrestored by extracting only the original data in downsampling at thereproduction.

While in this embodiment the signals of the three channels areillustrated for simplicity, more channels may be used.

While in this embodiment the Lossless compression is conducted whencompressing the data, the present invention is applicable to anapparatus which employs irreversible compression according to MPEGstandard or an acoustic processing apparatus such as an equalizer. Also,in this case, the amount of operation by the apparatus can be reduced,because processing by the same is reduced.

Industrial Availability

The signal processing apparatus of the present invention is capable ofreducing the amount of operation in decoding when reproducing aplurality of signals of different sampling frequencies.

What is claimed is:
 1. A signal processing apparatus for encoding aplurality of channel signals of different sampling frequencies to berecorded in a recording medium, said apparatus comprising: upsamplingmeans for transforming a sampling frequency of a channel signal having asmall sampling frequency among the plurality of channel signals ofdifferent sampling frequencies into a sampling frequency of a channelsignal having a large sampling frequency; a half band filter forreceiving a channel signal upsampled by said upsampling means as aninput and for eliminating unnecessary band signals from the receivedchannel signal; and format transformation means for transforming achannel signal processed by said half band filter and a channel signalhaving the large sampling frequency into signals having predeterminedformats.
 2. The signal processing apparatus of claim 1, furthercomprising: data compression means for performing lossless compressionof a signal processed by said half band filter and a channel signalhaving the large sampling frequency.
 3. The signal processing apparatusof claim 1, further comprising: upsampling information description meansfor describing upsampling information indicating that a sample of achannel signal processed by said half band filter is a sample beforeupsampling performed by said upsampling means, said upsamplinginformation to be recorded in a predetermined area of such recordingmedium.
 4. A signal processing apparatus for performing decoding toreproduce data recorded in a recording medium without filtering suchrecorded data, such data being recorded in such recording medium after asampling frequency of at least one channel signal among a plurality ofchannel signals having different sampling frequencies is upsampled as aresulting channel signal, and the resulting channel signal is processedby a half band filter and then transformed into a signal having apredetermined format, said apparatus comprising: data reading means forreading data from such recording medium; format inverse-transformationmeans for inversely transforming data read from said data reading meansinto a signal having a predetermined format; downsampling means fordownsampling a sampling frequency of a specified signal among the formatinverse-transformed signals; and downsampling control means forinstructing said downsampling means to read intermittently a specifiedsignal among the format inverse-transformed signals.
 5. The signalprocessing apparatus of claim 4, wherein said data reading means is forreading a signal that is completely reproducible data that has beensubjected to lossless compression, the signal processing apparatusfurther comprising: data decompression means for decompressingcompressed data into decompressed data after said compressed data issubjected to format inverse-transformation.
 6. The signal processingapparatus of claim 4, further comprising: upsampling informationextraction means for detecting upsampling information indicating thatdata is a sample before upsampling performed by said upsampling meanswhen detecting the upsampled signal data; and downsampling control meansfor instructing said downsampling means to read intermittently such dataaccording to the upsampling information.
 7. The signal processingapparatus of claim 6, further comprising recording means for recordingsaid upsampling information in a predetermined area of such recordingmedium as information indicating that data is a sample before upsamplingperformed by the upsampling means, and said downsampling means is forreading one of odd-numbered data and even-numbered data according tosaid upsampling information, thereby performing said intermittentreading.